1. Field of the Invention
The present invention relates to a sensor module according to the preamble of claim 1. Such a sensor module is known from the DE 43 31 574 A1. The invention relates to an infrared sensor module particularly applicable to cooking, baking and heating apparatuses, for example in microwave ovens.
2. Brief Description of Related Developments
FIG. 1 is a schematic block diagram as described in the above state of the art. 12 denotes the actual sensor element which is radiation-sensitive and outputs an electric signal to its clamps when electromagnetic radiation is incident. It may, for example, be a thermocouple. An amplifier 13 amplifies the electric signal of the sensor element. For balancing physically induced influences of the ambient temperature on the output signal of the sensor element, a reference means (14, 15) is further provided which is also temperature-sensitive. 14 denotes a temperature reference sensor, preferably a thermal resistor provided near the sensor and changing its parameters in accordance with its temperature. 15 denotes an amplifier or impedance converter converting said change into a usable electric signal which, combined with the amplified signal of the sensor element, reduces the influence of the ambient temperature on the signal from the radiation sensor. 16 denotes a different amplifier obtaining the difference between the signals from the radiation senor (12, 13) and the temperature sensor (14, 15) and outputting an approximately ambient temperature-compensated and object temperature-dependent output signal 11.
The known circuit has various disadvantages: The temperature compensation acts optimally only for a relatively small ambient temperature range since the characteristics of known miniaturised temperature reference elements are typically linear or exponential while a dependence with about the 4th power has proved particularly favourable. The signal amplification and processing are provided on a circuit board outside of the transistor housing in which the sensor chip and the temperature reference sensor are disposed. Since the sensor module is comparably large, space problems may occur in the integration in appliances. Above that the construction with the signal processing outside the metallic sensor housing may also lead to a falsification of the signal by electromagnetic interferences. This influence needs to be eliminated by expensive and complicated shielding measures or a subsequent signal processing.
It is the object of the invention to provide a sensor module capable of outputting an accurately temperature-compensated output signal corresponding to the temperature of an object. Said object is solved by the features of claim 1. The dependent claims are directed to preferred embodiments of the invention.